I feel that Thomas Walsh was small beer and not connected in any meaningful way with John Walsh of the Clan-na-Gael, who on 4th June 1888 sailed with McKenna from Le Havre to New York

The name Roger McKenna does appear to be an error. As I mentioned before, everytime I come across him he's referred to as Joseph or Joseph Patrick McKenna.

Here he is again, New York Times, 5th June 1888–

"Joseph Patrick McKenna, a member of the Lodge No. 96 of the Clan-na-Gael of Chicago, is said to have been assisting [John] Walsh. While in Paris McKenna lodged at the Hotel Boulevard St. Michael, registering as John Sylvester . . ."

I don't yet know enough about McKenna to make a judgement, but I would venture to suggest that Tumblety was an opportunist and survivor who was far too self-obsessed to align himself with any cause other than one of his own creation, and far too canny to ever make the fatal mistake of paying lip service to the Fenians.